In monocrystalline silicon, atoms are periodically arranged according to a specified rule. In fabricating monocrystalline silicon, silicon metal having a purity of 99.999999999% (totally 11 digits of “9” used to express the purity) is fused in a quartz crucible. Next, a seed crystal is inserted into the liquid silicon, rotated at a speed of 2-20 rpm and slowly pulled up at a speed of 0.3-10 mm per minute to form a monocrystalline silicon ingot having a diameter of 4-8 inches. The abovementioned process is the so-called Czochralski method. The monocrystalline silicon-based solar cell has high efficiency and high reliability and has been widely used nowadays.
The fossil fuel power plants and nuclear power plants dominate power generation in Taiwan. Therefore, Taiwan relies on the imported coal and nuclear fuel very much. Recently, the price of petroleum is growing higher and higher. Further, the safety of nuclear power is worried by people because the nuclear power plants have been too old to operate safely in Taiwan. In order to reduce the dependence on imported coal and nuclear power generation, Taiwan pays much attention to renewable energies now.
Taiwan is a subtropical country having abundant sunshine. Further, Taiwan has mature semiconductor industry and plays a significant role in the global solar cell production. Therefore, Taiwan is very suitable to develop solar energy.
The current solar cell fabrication process includes the following steps: using the RCA process to clean the surface of the substrate; patterning the surface of the substrate; using an acidic solution to clean the patterned surface; using a diffusion process to fabricate a P-type or N-type semiconductor layer on the surface of the substrate; etching the edges of the substrate having experienced the abovementioned diffusion process; removing the oxide on the surface of the substrate; fabricating an antireflection layer on the surface of the substrate; and fabricating metal electrodes on the substrate. Whether a P-type or N-type semiconductor layer is fabricated in the abovementioned diffusion process depends on the conductivity type of the substrate. However, a P-type doped silicon substrate is normally used as the substrate, and a high-temperature diffusion process is used to fabricate an N-type doped semiconductor layer.
From the abovementioned description, it is leaned that a solar cell fabrication process includes many different fabrication processes. It is very important for solar cells to increase the efficiency and decrease fabrication cost in the fabrication process. It is particularly critical to enhance the antireflection performance. The antireflection function is usually achieved via etching the surface with an acidic solution or fabricating an antireflection layer on the surface, which needs many fabrication processes and increases the fabrication cost. Metal electrodes are fabricated after the antireflection layer is completed. However, the fabrication of the metal electrodes would decrease the performance of the antireflection layer, which should decrease light utilization and efficiency of the solar cell.